Other
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p53b..01m&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P53B-01
Other
[5418] Planetary Sciences: Solid Surface Planets / Heat Flow, [5440] Planetary Sciences: Solid Surface Planets / Magnetic Fields And Magnetism, [5480] Planetary Sciences: Solid Surface Planets / Volcanism, [6219] Planetary Sciences: Solar System Objects / Io
Scientific paper
Io, the innermost of the Galilean satellites, has a mean radius (1816 km) and density (3528 kg m-3) that are just a bit larger than values for Earth’s moon. But Io has a much larger core (350 to 900 km radius) and a global heat flow near 2 W m-2, exceeding the Moon’s heat flow by a factor of ~102, due to intense tidal heating. Little is known about the state of Io’s core or mantle. The surface equatorial magnitude of the dipole field is less than a few hundred nT, but higher-order fields are possible. The fraction of melt in Io’s upper mantle is predicted to be near 20% (decreasing with depth) to maximize steady-state tidal heating, but reports of peak lava temperatures above 1600 K, if correct, suggest a much greater melt fraction, and Io’s heat flow may not be in equilibrium with the current tidal heating rate. Heat flow from polar regions, key to distinguishing deep mantle from asthenospheric tidal heating, is not adequately measured. Recent work (Lainey et al. 2009) suggests that Io’s orbit (and hence Europa and Ganymede orbits) are currently evolving out of the Laplace resonance, but little is know about long-term orbital evolution of the coupled moons. Io’s triaxial figure is consistent with hydrostatic equilibrium but we lack adequate measurements of its topographic variability in space and time (i.e., tides). The crust must be sufficiently thick and cold to support the ~100 mountains ranging up to 17 km height, so the heat flow is dominated by volcanic advection rather than conduction. The high resurfacing rate puts the crust into a state of compression, raising mountains via thrust faulting. There are hundreds of intensely active volcanic centers on Io (and hundreds more that would be considered active on Earth), and they display a wide range of eruptive behaviors and morphologies. Voluminous eruptions of basaltic lava that have dramatically altered the surfaces of the terrestrial planets are active today on Io. About 10 active volcanic plumes more than 50 km high are typically detectable from visible imaging at any point in time, but gas may be venting from many other locations. SO2 frost covers much of Io’s surface but other constituents are poorly known. About 1 ton/s of material is escaping from Io and its nanobar atmosphere, forming the plasma torus and a banana-shaped neutral cloud, and affecting the entire Jovian magnetospheric environment. Io’s exosphere includes ionized and atomic S, O, and Cl; atomic Na and K; molecular SO2, sulfur, and NaCl, but we lack a complete inventory of species escaping from Io and their source regions. Key questions about Io and its environment can be addressed by well-instrumented spacecraft in Jupiter orbit, making a series of carefully planned close flybys of Io combined with distant monitoring.
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